Function.prototype.partial = function(){
    var fn = this, args = Array.prototype.slice.call(arguments);
    return function(){
      var arg = 0;
      for ( var i = 0; i < args.length && arg < arguments.length; i++ )
        if ( args[i] === undefined )
          args[i] = arguments[arg++];
      return fn.apply(this, args);
    };
};
